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74 lines
3.2 KiB
HTML
74 lines
3.2 KiB
HTML
4 years ago
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<title>Compound Lvalues - GNU Compiler Collection (GCC) Internals</title>
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<meta name="description" content="GNU Compiler Collection (GCC) Internals">
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<link rel="up" href="Operands.html#Operands" title="Operands">
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<link rel="prev" href="Compound-Expressions.html#Compound-Expressions" title="Compound Expressions">
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<link rel="next" href="Conditional-Expressions.html#Conditional-Expressions" title="Conditional Expressions">
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Copyright (C) 1988-2015 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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<body>
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<div class="node">
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<a name="Compound-Lvalues"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Conditional-Expressions.html#Conditional-Expressions">Conditional Expressions</a>,
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Previous: <a rel="previous" accesskey="p" href="Compound-Expressions.html#Compound-Expressions">Compound Expressions</a>,
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Up: <a rel="up" accesskey="u" href="Operands.html#Operands">Operands</a>
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<hr>
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</div>
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<h4 class="subsection">11.6.2 Compound Lvalues</h4>
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<p><a name="index-Compound-Lvalues-2142"></a>
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Currently compound lvalues involving array and structure field references
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are not broken down; an expression like <code>a.b[2] = 42</code> is not reduced
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any further (though complex array subscripts are). This restriction is a
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workaround for limitations in later optimizers; if we were to convert this
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to
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<pre class="smallexample"> T1 = &a.b;
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T1[2] = 42;
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</pre>
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<p>alias analysis would not remember that the reference to <code>T1[2]</code> came
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by way of <code>a.b</code>, so it would think that the assignment could alias
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another member of <code>a</code>; this broke <code>struct-alias-1.c</code>. Future
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optimizer improvements may make this limitation unnecessary.
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</body></html>
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